BiBr e

CiCr e

1/2

1/2

2 ( ) 2integer

3.4 1

2arcsin

B C

B

V

LC

U L

k E d nn

eVE E

E EE E

Alternative representation of QWPhase accumulation model

Dispersion of k(E)

FEVBME

5.5VE eV

2.1gV eV

1/221

2 1

2 2

1/2

22

4 ( )

2

2

2( )

G G G G VBM

G G VBM

G

r V E E V E E

r E V E E r

h GEm

m rk Eh

Synchrotron radiation photoemission spectroscopy

• ISA Aarhus University• Maximum Energy 580 MeV• Max Current 250 mA• Lifetime 15 hours

SGM130-400 eV1010 photons/sec @130 eV

Photoelectron spectroscopy• Core levels

– Chemical reactions/mixing– Growth modes

• Valence bands– Electronic levels relevant for optics

Binding Energy(eV)

sp band

h=130 eV

Secondaryelectrons

Inte

nsity

(arb

. uni

ts) Al2p

h

EF E

vac

Kinetic Energy (eV)

Scanning film thickness by movingwedge through laser or synchrotron beam

Wedge-shaped metal film

18 18 2. . mSample moved into shadow of shield. Evaporation rate ~1 ML per minute Triangular domains ~200 nm

Ag(111) LEED-pattern - only one type of domains

38,80 38,85 38,90 38,95 39,000

5

10

15

20

25Convolution fit ofGauss beamand step functiond=150 m

Si2

p pe

ak h

eigh

t (ar

b. u

nits

)

Sample position (mm)

Width of synchrotron beam

AFM

Film growth - Si2p spectra

102 101 100 99 98

0

2

4

6

8

10

101 100 99 98 97

Growth at 170 KNo annealing

130 eV

Inte

nsity

(arb

. uni

ts)

7x7

Growth at 170 KAnnealing atroom temperature

Binding Energy (eV)

0 2 4 6 8 10 120,01

0,1

1

10 Bulk 300 K Surface 300 K Bulk 170 K Surface 170 K

Inte

nsity

(ar

b. u

nits

)

Coverage (ML)

Growth at 170 K leads to exponential decay of Si2p levels with ~5Å decay rate.Room temperature annealing of the film leads to growth of large atomically flatdomains. Areas with low Ag coverage are formed.

Annealing

3,0 2,5 2,0 1,5 1,0 0,5 0,00

5

10

15

20

25

30

Double peaks

14

2418

1297

5

4210

Cu VBM

Clean Si(111)7x7

Inte

nsity

(ar

b. u

nits

)

Binding Energy (eV)

Cu buffer layerCu wedge under 10-ML Ag film

3 ML Cu: disordered film

6-7 ML Cu: optimum for Ag overlayer

> 7 ML Cu: coupling of overlayerand substrate levels -double peaks -avoided crossings

6 4 2 01

2

3

4

5

6

7

8

9

3 2 1 00,0

0,5

1,0

1,5

2,0

2,5

3,0Ag / 6 ML Cu / Si(111) Valence band 47 eV

20 ML Ag

6 ML Cu

Inte

nsity

(ar

b. u

nits

)

Binding Energy (eV)

Effect of Cu buffer layer

QW levels and film roughness

0 2 4 6 8 10 12 14 16 18 20 22 24-2.5

-2

-1.5

-1

-0.5

0

Thickness (ML)

Bin

ding

Ene

rgy

(eV

)

Film thickness variations expected within probed areaVariations within a few atomic layer give broad peaks in photoemission

Beam size on sample ~1 mm